This task order is to facilitate the conduct of clinical research on Ebola and other emerging and re-emerging infectious diseases, and to continue the development of clinical research infrastructure in Liberia and Mali. The Ebola research follows the PREVAC (Partnership for Research on Ebola Vaccination) protocol. PREVAC is a randomized, double-blind, two-stage trial comparing three experimental Ebola vaccine strategies with identical placebo regimens. For Version 4.0 of PREVAC, the primary objectives are to compare each of the three vaccine strategies with the pooled placebo group (3 pair-wise comparisons) for safety and immunogenicity. These evaluations will be performed separately in adults and children.